The present invention relates to a jet printing ink and an ink image-forming method using an ink jet printer.
An ink-jet recording method has been developed and widely used because it has various merits. For example, materials for the method are available at a low cost, and high speed recording can be accomplished. Further, the method makes relatively low noise, and easily utilizable for full-color recording.
As the ink-jet recording method, three types are known. One is a method in which drops of ink are ejected under pressure by means of a piezoelectric element. In another method, bubbles are formed in ink by heating so that the bubbles would push out drops of the ink. The other is a method in which drops of ink are sucked and ejected with electrostatic force. As the ink for the method (i.e., jet printing ink), various kinds of ink such as aqueous ink, oily ink, and solid (melting) ink have been used.
Dyes used for the ink should satisfy various conditions. For example, they should be highly soluble in a solvent, and they should have excellent hues. It is also necessary for the dyes to have high resistance against light, heat, air, water and chemicals. Further, they should be well fixed onto an image-receiving sheet without blotting. They are furthermore required to have long shelf lives, to have no toxicity, to have high purity, and to be available at a low cost.
The above-mentioned requirements ought to be considered in ink-jet printing systems not only using receiving sheets designed for the specific ink-jet printing system but also using an ordinary paper sheets such as a coated paper sheet for electrostatic duplicating system or a recycled paper sheet. In more detail, it is important for ink-jet printing system that these ordinary paper sheets are employable as the image receiving sheets. Therefore, an ink-jet printing ink should form a clear image not only on a specifically designed paper sheet but also in an ordinary paper.
It is an object of the present invention to provide an improved jet printing ink and an ink-jet recording method, which forms a clear image not only on a specifically designed paper sheet but also in an ordinary paper.
It is another object of the invention to provide an improved jet printing ink which forms a clear image with good hue, high resistance to light, and fixation to a variety of paper sheets.
There is provided by the invention a jet printing ink containing a jet printing ink comprising a dye and an aqueous medium, which further comprises a basic polymer having a side-chain containing a tertiary amino group, a quaternary ammonium group, or a nitrogen atom-containing heterocyclic group.
There is further provided by the invention a method of forming an ink image on a receiving sheet using an ink jet printer of the invention.
In the invention, the basic polymer preferably contains a repeating unit of the following formula (I): 
in which R is a hydrogen atom or methyl; L is a single bond, xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94, an alkylene group, an arylene group, or a combination thereof; and Am is a tertiary amino group, a quaternary ammonium group, or a nitrogen atom-containing heterocyclic group.
Particularly preferred basic polymer has a side-chain containing a nitrogen atom-containing heterocyclic group, such as 1-imidazolyl.
The basic polymer preferably has a molecular weight (weight average molecular weight: Mw) in the range of 1,000 to 100,000, and is contained preferably in an amount of 0.1 to 50 weight %, based on the amount of ink, so that the resulting ink has a viscosity of 50 cp or lower at 25xc2x0 C.
In the jet printing ink of the invention, the dye preferably is an azomethine dye or an azo dye.